(1) Field of the Invention.
The present invention relates generally to a trailer arrangement such as a tractor trailer unit and more particularly to the steering of a tractor trailer unit by turning the wheels of the trailer to increase the maneuverability of the entire unit during parking and operation under close clearance conditions. More particularly still the present invention relates to the operation of tandem or dual axle tractor trailer assemblies or other truck-type vehicles having dual rear axles wherein one or more sets of the wheels on the trailer itself may be steered to provide additional maneuverability in congested traffic, narrow streets and other conditions.
2. Description of the Prior Art.
Tractor trailer assemblies are widely used for the transport of goods over both short and long distances. In order to be economical, such tractor trailer assemblies should have as much capacity as possible. However, road regulations limit the amount of weight which can be accommodated upon a single wheel in order to prevent too much stress from being placed upon a single point upon a highway. Too much stress or weight upon a single point on a highway seriously increases the risk of cracking of the pavement of such highway due to differential stress which tends to force one paving section downwardly while adjoining sections are in effect forced upwardly by adjacent ground pressure Excess pressure i.e. excess weight, applied at a single point or few points upon a highway is generally avoided or relieved by providing multiple wheels upon a truck in order to spread the weight of the truck over as many road contacting points as possible. As is well known to those skilled in the art as well as the general public using the highways, most tractor trailers incorporate at least two separate rear axles, each of which preferably accommodates on each side two large truck wheels and associated tires. A conventional large trailer wheel arrangement therefore distributes the weight of the rear portion of the trailer of a tractor trailer combination over eight separate road contacting points. Additional axles and additional individual tires may be incorporated for particuarly severe load conditions. In particular, and especially with very heavy trucks such as earth and rock-bearing trucks, a third axle may be present, the wheels of which only come into contact with the road surface when the truck is heavily loaded so as to compress the normal suspension sufficiently to bring the auxiliary wheels into contact with the highway. Alternatively, the third axle may be actively lifted from the road surface when not required for weight-bearing purposes.
It is normally desirable to have multiple axles on a truck such as the trailer portion of a tractor trailer assembly spaced from each other along the truck or trailer body in order to distribute the weight of the truck and/or cargo over as wide a portion of the road surface or paving as possible so as to decrease the loading upon any single portion of the road paving, thereby decreasing the tendency of such paving to crack. Since, however, it is necessary for a truck to proceed not only in a straight path, but to deviate from such path to one side or the other, i.e. to turn, it becomes impractical to have the axles spaced far apart since during turning the rear of the truck will pivot either about the rear wheels tending to drag the forward wheels to the side over the road surface or the rear of the trailer assembly will tend to pivot about the set of wheels on the forward axle tending to drag and scuff the tires on the rear axle sidewise across the ground or road surface. In either case, the scuffing and dragging of tires of the wheels on one axle to the side very seriously increases the wear and stress upon the tires and also undesirably stresses the entire truck structure. Which set of tires will be scuffed or dragged sidewise across the ground will depend largely upon the relative spacing of the sets of tires upon the axles of the trailer and the relative weight carried by each axle. If the weight is substantially equal, pivoting of the trailer will usually be about the rear wheels and the forward set of wheels on the forward rear axle will be dragged sidewise as the truck turns, scuffing and wearing out the tires on these wheels. However, if the loading should be greater upon the forward set of wheels due to misadjustment of the weight of the truck or the suspension of the wheels, the turning radius will tend to be about the front set of rear wheels of the truck rather than about the second set of rear wheels of the truck. In this case the rear tires on the truck will tend to be dragged sideways across the road surface and scuffed causing undue wear of the tires and decreasing their service life as well as unduly stressing the structure of the tractor trailer itself. This sidewise movement problem has been recognized for many years, and many schemes for alleviating the scuffing and wear of one or both sets of tires have been suggested. The simplest and the most universally used alleviation scheme involves minimum spacing between the two axles since the farther the axles are spaced from each other, the more one or the other set of tires will be scuffed and dragged sideways upon turning of the truck. In other words, as the axles are moved toward each other, the relative difference in sideways deflection becomes progressively less and if the movement of the tires toward each other could be continued to the ultimate by merging the tires of one axle with the tires of the other axle rendering the two coextensive, no differential sideways movement would occur and no scuffing would take place. Obviously, as a practical matter such close spacing of the tires is unattainable and the closest practical spacing is to have the tires of adjacent wheels within a few inches of each other. Such positioning of the wheels or tires provides the minimum amount of scuffing of the tires upon turning. However, as pointed out above, it also minimizes the advantage gained by spacing the axles so as to space the contact points of the tires upon the road surface and minimize possible cracking of the road surface due to overloading at a particular point on such road surface.
The second most widely suggested expedient to reduce or eliminate scuffing and wear on one set of tires is to provide a turning mechanism for one or more of the axles, or alternatively, for the individual wheels upon the axles, so the tires on the wheels are not dragged across the road surface. If the tires are turned or oriented in the direction of their movement, the wear on the tires can be substantially decreased since the tires and accompanying wheels will be able to rotate about their rotational axes as the wheel and tire is moved over the road surface thus relieving considerable abrasion upon the tires. A large number of schemes have been proposed for steering one or the other of the rear axles of a dual axle truck or tractor trailer assembly in accordance with such general principle.
For example, early arrangements for turning or steering the front set of a dual rear wheel arrangement on an automotive vehicle in order to prevent excessive wear of the tires of such vehicle are set forth in patents 842,245 issued Jan. 29, 1907 and 880,737 issued May 26, 1908 to C. T. Pratt, both for steered axle assemblies for automobiles. The same type of arrangement was applied to a truck type assembly in U.S. Pat. No. 915,733 issued Mar. 23, 1909 to A. E. Brillie. In the Brillie arrangement the wheels on the rearmost axle of the two rear axles turn while the forward-most wheels on the rear of the truck are held stationary with respect to their alignment with the truck body. A further modification involving the steering of the front wheels of a rear truck bogie, or dual wheel mounting, of a tractor trailer is shown in U.S. Pat. No. 1,120,188 issued Dec. 8, 1914 to G. Felty. In this case it is the forward set of a fairly closely spaced set of trailer wheels on a separate bogie which turn. A similar arrangement is shown in U.S. Pat. No. 1,559,050 issued Oct. 27, 1925 to 0. D. Schvartz.
Not only have the rear wheels of tractor trailer units and truck units tended to skid or scuff when the vehicles turn, but when dual rear axles with multiple wheels on said axles are used on a truck with the axles fixed generally perpendicular to the longitudinal center line of the vehicle, they have a tendency to cause the entire vehicle to move straight ahead even though the front steering wheels are turned. As a result, both the front, or steering, wheels and the rear wheels have had a tendency to skid when making a turn. This is known generally in the trade as "plowing". Such plowing tendency of the wheels results in an undesirable wear of all of the tires and also makes steering difficult. The use of a tractor trailer arrangement, of course, tends to alleviate plowing of the front or steering wheels since the tractor portion of the truck can turn independently of the trailer portion. However, tractor trailer combinations are subject in some respects to an even more serious problem when there are dual wheels on the trailer since such dual wheels tend also to maintain the trailer moving in a longitudinal straight line. In slippery or other insecure conditions this can easily lead to the phenomena known as "jackknifing" in which the forward momentum of the trailer is applied at an angle to the pivot point of the trailer with the tractor at the location of the so-called "fifth wheel" as the unit turns so that the weight and the momentum of the trailer tends to force the rear of the tractor around in an arc until the tractor portion of the truck is facing almost opposite to the orientation of the trailer portion of the truck. As soon as the tractor portion and the trailer portion of a truck reach an angle close to or greater than a right angle at highway speeds, the tractor has no further control of the trailer. Many serious accidents have resulted and continue to result from jackknifing phenomena.
Since the phenomena of scuffing and tire wear on tractor trailers and "plowing" in unitary large truck constructions are well known problems which have very serious economic and safety ramifications, a great deal of thought has, as pointed out above, been put into developing solutions for such problems by many prior inventors. It has been realized that one way to alleviate such problems would be to make the rear wheels of a dual axle truck either independently steerable or one or more of the rear axles as a unit steerable so that the rear wheels could be either pointed in the direction of movement to alleviate scuffing or could be arranged to steer in the opposite direction in coordination with the steering on the front wheels to maintain a more uniform forwardly oriented movement of the entire vehicle. The usual proposal has been to make the rearmost axles steerable in the same way that the front axle is steerable and to coordinate such rear steering with the front axle so that the rear axle steers in a uniform manner in the opposite direction. Such arrangements have not proved particularly successful and have not come into widespread use due to cost considerations and to the general weakening of the structure entailed by installing the necessary pivots, king pins and the like to facilitate the rear steering action. U. S. Pat. No. 3,930,669 issued Jan. 6, 1976 to Kollander et al. lists in the background of the invention a number of prior patents in which various forms of steerable rear wheels on trailers have been proposed. Furthermore, the list provided by Kollander et al. is only a very partial list of the disclosures to be found in this art. One patent of note is U.S. Pat. No. 3,533,644, issued Oct. 13, 1970 to C. E. Humes which discloses a trailer steering arrangement particularly for alleviating jackknifing. The Hume arrangement uses air-bag-type suspensions on his rotating axles.
In spite of the seriousness of the problems addressed and, therefore, the plurality of solutions proposed in the various prior art references, none of the prior proposals have come into general or, in most cases, even partial use due to certain impracticalities which have been inherent in previous schemes.
Tire wear and handling difficulties due to scuffing during turning, as well as plowing and accidents caused by jackknifing, are by no means the only difficulties implicit in present tractor trailer construction with dual fixed or multiple fixed rear axle constructions. As is well known to those skilled in the art, such tractor trailer arrangements are very difficult to steer in close quarters, particularly when the tractor trailer is large. It is, for example, very difficult to park a tractor trailer combination in a small space or to make turns into narrow streets or other close quarters due to the wide turns which a long tractor trailer combination must make and the inability of the rear load bearing wheels on a trailer to track reliably along the path of the wheels of the tractor. In other words, the rear wheels tend to track more or less directly toward the location of the pivot point of the trailer with the tractor. However, when a sharp turn must be made, the rear axles of the trailer are so far behind the rear axles of the tractor that when negotiating a sharp curve or turn the pivot point between the tractor and the trailer will often have passed around the corner before the rear axles of the trailer even reach the corner. Since, therefore, the rear axles tend to track toward the pivot point of the articulated tractor trailer unit, the rear axles will tend to be drawn into any intervening structure, vehicles or the like which may occupy the corner about which the tractor trailer combination is attempting to turn. Similar difficulties with hook-and-ladder-type fire apparatus, which often must operate in constricted circumstances, have been solved in the past, as is well known in the art and to the general public, by the provision of a special steering station at the rear of the trailer portion of the hook and ladder apparatus, which steering station is manned by a fireman who deliberately steers the rear of the trailer independently about a corner. It will be obvious, however, that a similar arrangement is impractical in tractor trailer combinations in which the major use of the tractor trailer combination is over fairly open highways where such auxiliary steering has no particular use and in which the additional expense of an extra driver to steer the rear of the truck would be economically unfeasible due not only to the extra wages required for compensation of the additional driver, but due to the loss of valuable cargo space incumbent upon the provision of a steering location for an extra driver in the truck structure. Nevertheless, various proposals for providing other steering arrangements have been made in an attempt to provide better maneuverability for the rear portion of not only tractor trailer combinations, but other vehicle types in which difficulty with close-quarter steering and/or parking may be encountered. One solution proposed by some inventors with respect to such close-quarter steering difficulties has been the use of auxiliary wheels which may be normally maintained in retracted position and used only in contact with the ground or road surface when it is desired to move the rear of the truck or other vehicle in a direction contrary to the normal direction in which the wheels of the truck normally track.
Since, as pointed out above, the wheels of the trailer unit of a tractor trailer combination turning a corner follow inside of the curve of the path taken by the tractor unit, the driver, when negotiating a sharp corner, must make a very wide swing with the tractor in order to insure that the rear of the trailer will not cut across the corner thereby running the risk of side swiping any vehicle or other object or structure standing, parked or located inside the trailer's path of travel. Indeed, most automobile drivers have observed large trailer trucks making such wide swings around a corner and have quite likely, at one time or another, been concerned that their own vehicle would be struck by either the tractor swinging wide of the center of the road or by the trailer cutting across the opposite inside corner of the road. Such difficulties are exaggerated by the use of double trailer combinations with the result that many states do not allow plural trailers, and even when they do allow such plural trailers, often restrict them to interstate highways and adjacent feeder road systems. In order to negotiate such sharp turns, it is necessary that the rear wheels of the trailer be turned in the opposite direction from the steering wheels of the tractor unit so that the rear of the trailer is drawn in a wide arc about the curve comparable to the arc taken by the tractor unit. An arrangement for thus steering the rear wheels of a tractor trailer combination is disclosed in U.S. Pat. 3,533,645 issued Oct. 13, 1970 to M. W. Newberry. Other arrangements have been provided by other inventors.
An arrangement for facilitating parking of articulated vehicles such as tractor trailers and the like is shown in U.S. Pat. No. 4,616,726 issued Oct. 14, 1986 to Johansson who provides an auxiliary set of wheels which may be urged into contact with the ground temporarily lifting a normal driving wheel and allowing the rear of a truck to be swung to the side without any forward movement of said truck.
It will be evident from the foregoing discussion that there have been two main problems with large tractor trailer and other large truck combinations so far as negotiating curves and turns is concerned. The first involves tire scuffing and plowing and/or jackknifing resulting from the use of dual sets of fixed axles at the rear of a truck or trailer and the second is the lack of maneuverability in close quarters of lengthy trucks and particularly tractor trailer combinations whether dual axle or single axle. The proposed solutions for the two problems have, furthermore, followed related, but distinct paths. In the case of tire wear, scuffing and plowing, the proposed solution, other than keeping dual or multiple axles as close together as possible, has been to turn at least one set of wheels in the natural direction of movement to facilitate rotation of the wheels of their axles rather than dragging of such wheel over the road surface. In the case of the problem encountered in turning or maneuvering a large truck in a small space, on the other hand, the usual solution suggested, other than the provision of auxiliary wheels for movement at angles to the natural rotation of the regular wheels, has been to turn the rear axles in the opposite direction from the front or steering wheels to facilitate more accurate tracking of the rear of the truck after or in the path of the forward portion.
A further difficulty with tandem or multiple axle truck arrangements is unequal distribution of weight between the axles during operation. If the weight of the vehicle is not equally supported by the tandem axles, particuarly on rough ground or road surfaces, there is always a danger of structural failure or instability of the vehicle to such an extent as to possibly even tip over such vehicle. Various arrangements for equalization of load have been used in the past including metal compression springs, air springs, rubber springs, various equalizing levers, and other arrangements. One fairly successful arrangement frequently used on modern trucks is a pneumatic suspension arrangement which may be either manually or automatically adjusted and leveled so that all axles carry substantially equal weights to prevent damage to the truck structure and/or in stability of the truck during operation. Such arrangements have not, however, solved the problems of steering the rear of a truck in close quarters. The Humes U.S. Pat. No. 3,533,644, noted above, discloses such a suspension system. Sometimes trucks have used such pneumatic suspension systems to actually lift one set or one axle of truck wheels entirely from the road surface. U.S. Pat. No. 3,285,621 issued Nov. 16, 1966 to Turner can be mentioned as an example of such an arrangement. In the Turner patent, auxiliary wheel axles may be forced downwardly into contact with the road surface by a pneumatic suspension arrangement when a heavy load is carried, but may be raised by appropriate means when a light load is carried to decrease tire wear and scuffing when the truck rounds corners.
There has been a need, therefore, for a steering arrangement for the rear of the trailer of a tractor trailer combination which would allow such trailer to be easily maneuvered in close quarters and about sharp turns. In order to be practical, such steering arrangement should be simple to operate, foolproof, and easily and cheaply mounted upon the trailer of a tractor trailer combination. Furthermore, since many trucks are owned by small operators, it is desirable that any such rear trailer steering arrangement be mountable upon the truck structure by the owner of the truck or by fairly small truck servicing organizations as well as being incorporable into the trucks' structure during manufacture of new trucks. In other words, it is very highly desirable that any such steering arrangement be retrofitable into trucks already upon the highway with a minimum of mechanical modifications as well as being easily incorporated into the design of trucks yet to be built. It is, furthermore, highly desirable that such steering arrangement eliminate, as much as possible, undesirable scuffing and tire wear during use to steer the truck in close quarters.